1 reply to this topic

[renogan]

Hi, i am currently working on separation of acetone/water mixture using a batch distillation column. How do u go about calculating the packing required for the batch distillation column? What factors must i consider? In this case can we still use the McCabe-Thiele method??

Thanx

[siretb]

In a batch distillation, the holdup on each tray, or in each segment of packing is a critical parameter. You need to take this into account!
You need to dertermine how many theoretical stages you need for onee thing, but also the distillate rate and how quicly the sump composition varies with time.
I would advise that you use a simulation program like Batchfrac, now part of the ASPEN Bundle.

You may refer to Perry's handbook 7th Edition pages 13-97+, where they give a method

In a batch distillation, one usually wants to have a given puruty in an accumulator or reservoir, and one often varies the reflux ratio, and sometimes the pressure. (sometimes, one operates also at a fixed reflux ratio and lets the distillate quality vary)
If you have no access to a simulation program, a Mac Cabe & Thiel approach can be of some help.
One approach, but not the only one will be to keep the distillate compostion constant for a while, so you select the desired purity, do a first calculation with the initial sump (reboiler) composition and determine the number of stages and reflux ratio. Be conservative and select twice as much stages as the minimum number of stages. Then, with the selected number of stages see how much you can deplete the sump from the light component before you have to increase too much the reflux ratio.
For a packed tower see how much holdup you have at start and at the end (the holdup will vary because the reflux ratio varies.
Then do an intermediate cut, and skip to the second lightest component.